Earlier quoted context omitted.
I'd go further and suggest that a lot of atheists would echo the hope that there is some kind of fabulous immortality beyond the grave, it's just that the concept is, upon examination, absurd.
Eternal life holds no interest for me. Imagine living a million years, seeing and thinking all there is to see and think, then living a billion years after that. Then you realize that you're precisely 0% of the way to the finish line. Long after the heat death of the universe, a consciousness with nothing to cogitate. No thanks.
If you argue from a base mechanics point of view (e.g. Your brain is basically a hard drive with n bits of storage an thus can only enter 2^n states) then you're assuming that in this hypothetical afterlife your physical limitations are maintained. Since your basic assumptions about the universe have been demonstrated to be wrong, assuming this particular assumption will be correct is drawing a very long bow. And the initial assumption is very much in doubt.
To my mind an atheist is someone who has yet to encounter a plausible religion, not (a) someone who defines their beliefs in opposition to one religion (e.g. I do not believ heaven is a green pasture populated by angels playing harps and dead Christians tending sheep) or (b) someone who is closed to the possibility that a plausible religion might exist.